Because of the ease of access, dynamics of application, large surface area, vast exposure to the circulatory and lymphatic networks, and non-invasive nature of the treatment, the delivery of pharmaceutically-active agents through the skin has long been a promising concept. This is true whether the bioavailability desired is systemic or dermal, regional or local.
The advantages of this form of delivery include, but are not limited to: avoidance of the risks associated with parenteral treatment; elimination of the inconveniences of parenteral treatment; avoidance of the variable rates of absorption and metabolism inherent in oral treatment; increasing the continuity of drug administration by permitting delivery of agents with short biological half-lives; and elimination of gastrointestinal irritation resulting from exposing the gastrointestinal tract to pharmaceutical actives, preservatives, tableting agents, and the like. Most importantly, topical delivery possesses the potential for effectively treating conditions which are local in nature (or which exhibit local manifestations), systemically as well as locally with the same treatment regimen. Thus, effective compositions to deliver pharmaceutical agents are highly sought after.
However, because it must serve as a barrier to the ingress of pathogens and toxic materials, and the egress of physiologic fluids, the skin is highly impermeable. It must be impermeable to preserve its own integrity while at the same time maintaining the delicate dynamic electrolyte balance of the body. The skin must serve a containment function; it must also function as a microbial, chemical, radiation and thermal barrier.
A good deal of this impermeability of the skin results from the nature of one very thin layer created by normal developmental and physiological changes in the skin. After cells are formed in the basal layer, they begin to migrate toward the skin surface, until they are eventually sloughed off. As they undergo this migration, they become progressively more dehydrated and keratinized. When they reach the surface, just prior to being discarded, they form a thin layer of dense, metabolically inactive cells approximately ten microns (10-15 cells) thick. This layer is called the stratum corneum or the "cornfield layer". As a result of the high degree of keratinization of the cells which comprise the stratum corneum, a formidable barrier is created. Therefore, penetration via the nonpolar route, i.e., across the membrane of these cells, remains most difficult.
Other possible penetration routes are available. First, any mechanism which allows the egress of materials, e.g. the sebaceous apparatus, can be manipulated to allow the ingress of materials. Second, the stratum corneum, though keratinized to a great degree, is composed of about 15% lipid-based intercellular material. This may offer a less formidable route despite the close packing of the cells.
It is known that certain binary skin penetration systems can increase the disorder of these lipids. By so increasing the disorder of the lipid portion of the cell-envelope in the stratum corneum, the lipid packing of the cells can be disrupted. This disruption allows certain pharmaceutically active agents to pass through the stratum corneum. This discovery has been confirmed by differential scanning calorimetery, indicating that certain binary skin penetration enhancement systems eliminate the Tm-2 peak associated with melting of cell-envelope lipids.
Adrenal corticosteroids, and the synthetic analogues thereof, are some of the most useful pharmaceutical actives known in the art. These compounds have the capacity to prevent the development of, or suppress existing, localized heat, redness, tenderness and swelling which characterizes any inflammation of skin or mucous membrane. The utility of these compounds is magnified in a clinical setting by the fact that corticosteroids inhibit this inflammatory response whether the inciting cause or agent is radiant, mechanical, chemical, infectious or immunological. Since the first recognition of the potent anti-inflammatory properties of these compounds in 1949, their therapeutic uses have increased dramatically. The unique biochemical, pharmacologic and physiologic properties of corticosteroids make them almost universally useful in the topical treatment of inflammatory conditions.
Corticosteroids are also useful in treating many conditions when used by systemic application. For example, their potent anti-inflammatory and immunosuppressive effects make them useful in the treatment of most rheumatic conditions and diseases.
While corticosteroids are highly effective in the treatment of the above systemic and local conditions, they suffer from one significant disadvantage. The size and shape of corticosteroids makes them exceedingly difficult to deliver percutaneously. Conventional and commercial topical steroid preparations are only marginally effective in delivering sufficient steroid for immediate treatment of local conditions; systemic steroid treatment by percutaneous delivery from known vehicles is virtually impossible. Accordingly, a vehicle system which increases both the level and speed of penetration of the steroid through the skin would be more efficient in the treatment of localized conditions and, more importantly, would greatly increase the chances of making systemic treatment by topical application viable. Effective systemic delivery of steroids by the topical mode of treatment is highly desirable since the topical treatment would result in a lower level of side effects than those associated with conventional (oral or parenteral) methods of administration when systemic steroid therapies are indicated.
It has now been discovered that steroids can be effectively delivered percutaneously by incorporating them into a specific vehicle which provides an exceptional increase in penetration over conventinal steroid vehicles, and, more surprisingly, at a rate which now makes the systemic method of administering steroids percutaneously a practical alternative. Specifically, it has been discovered that a select number of combinations of a binary penetration system comprising a cell-envelope disordering compound and a diol compound, heretofore thought only to be useful in delivering nonsteroidal varieties of anti-inflammatory actives and select substituted adenosine- and guanine-derived antivirals, can consistently and dramatically improve the topical delivery of certain corticosteroids, such as triamcinolone acetonide, when used in a vehicle or formulation which is free of certain common solvents, cosolvents, excipients and lipids other than the selected cell-envelope disordering compound.
U.S. Pat. No. 4,343,798, Fawzi, issued Aug. 10, 1982, describes topical antimicrobial/anti-inflammatory compositions containing C.sub.5 -C.sub.12 fatty acids in combination with corticosteroids.
U.S. Pat. No. 3,934,013, Poulsen, issued Jan. 20, 1976, describes topical pharmaceutical compositions containing at least two corticosteroids, propylene glycol, a fatty alcohol and water. The patentee describes the "fatty alcohol ingredient" as any fatty alcohol having from 16-24 carbon atoms and, preferably, as a saturated, monohydric primary alcohol such as cetyl alcohol, stearyl alcohol or behenal alcohol.
U.S. Pat. No. 4,289,764, Yarrow, et al., issued Sept. 15, 1981, describes topical pharmaceutical compositions with increased shelf stability. These compositions comprise a steroid, 15-50% by weight propylene glycol and are buffered to a pH of 2.7-3.3. The specification describes the desirability of thickening the propylene glycol (due to its low viscosity) with a compound selected from long-chain paraffins, fatty alcohols, and waxes, including cetyl stearyl alcohol, white soft paraffin and liquid paraffin.
U.S. Pat. No. 4,070,462, Ecker, issued Feb. 24, 1978, discloses a topical vehicle which includes (i) 5-15% 1,2-propanediol, 2,3-butanediol or 2-methyl-2,4, propanediol; (ii) 1-3% propylene glycol monostearate; and (iii) petrolatums and waxes to 100%.
U.S. patent application, Ser. No. 001,974, Wickett, et al., filed Jan. 8, 1979, describes compositions useful in the treatment of acne. These compositions contain benzoyl peroxide, C.sub.6 -C.sub.14 primary alcohols, and a diol selected from 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, and 2,3-butanediol. A foreign equivalent of this application was made available to the public July 23, 1980. See European Patent Application No. 13,459.
U.S. patent application Ser. No. 296,706, Cooper, et al., filed Aug. 27, 1981, describes compositions for topical application. These compositions described are suitable for effective delivery of lipophilic, pharmacologically active compounds using primary alcohols or various carboxylate compounds in combination with selected diols. See European Patent Application No. 43,738.
U.S. patent application Ser. No. 383,391, Cooper, filed June 1, 1982, discloses and claims a binary penetration system utilizing a diol and a cell-envelope disordering compound to aid in the penetration of 9-hydroxyethoxymethyl (and related) derivatives of 6- and 2,6-substituted purines. These purine compounds are reported to be effective in the treatment of viral infections, especially herpes, and can be administered parenterally, orally or topically. 9-(2-hydroxyethoxymethyl) guanine is disclosed as being particularly active.
1,2-propanediol ("propylene glycol") and the C.sub.10 -C.sub.14 alcohols have been used, separately, in cosmetic and pharmaceutical formulations. In particular, propylene glycol has been described in several articles in the literature as enhancing the penetration of certain pharmacologically active agents, such as the corticosteroids. See Rosuold, J., et al., "Effect of Formulation On In Vitro Release and In Vivo Absorption of Corticosteroids from Ointments", Medd. Novsk Favm Selsk, 44, 21-45 (1982); see also, Anjo, D. M., et al., "Methods for Predicting Percutaneous Penetration in Man", Percutaneous Absorption of Steroids. pp 31-51, Academic Press, New York, N.Y. (1980).
U.S. Pat. No. 3,535,422, Cox, et al., Oct. 20, 1970, relates to stable benzoyl peroxide compositions containing organic emollients. The compositions include emollients selected from the C.sub.4 -C.sub.20 aliphatic alcohols, C.sub.2 -C.sub.3 glycols, C.sub.12 -C.sub.20 fatty acids and their esters, and mixtures thereof.
U.S. Pat. No. 4,070,462, Ecker, issued Jan. 24, 1978, describes topical steroid compositions containing 6% propylene glycol and 1% propylene glycol monostearate.
Canadian Pat. No. 1,072,009, Sipos, issued Feb. 19, 1980, describes topical antimicrobial compositions containing C.sub.5 -C.sub.10 straight chain alcohols or C.sub.17 branched chain alcohols in which the longest chain is C.sub.5 -C.sub.10.
CA 92:153,181j; describes an indomethacin ointment containing 10% propylene glycol and 1.1% diisopropanolamine.
U.S. Pat. No. 2,990,331, Neumann, et al., issued June 27, 1961, describes tetracycline compositions containing carboxylic acid alkylolamides.
H. Barnes, et al., Br. J. Derm. 93, 459 (1975), describe testing of fluocinonide and fluocinolone acetonide in a vehicle described as fatty alcohol propylene glycol (FAPG).
P. J. W. Ayres, et al., Br. J. Derm., 99, 307 (1978), report comparative skin penetration of cortisol from commercially available cortisol ointments.
Schaaf and Gross, Dermatologica, 106, 357 (1953), note that unsaturated fatty acids and C.sub.6 -C.sub.14 saturated fatty acids are particularly active in provoking epidermal thickening.
J. Zatz, et al., J. Pharm. Sci., 67, 789 (1978), describe the effect of formulation factors on penetration of hydrocortisone through mouse skin.
S. K. Chandrasekaran, et al., J. Pharm. Sci., 67, 1370 (1978), discuss the pharmacokinetics of drug permeation through human skin.
B. Idson, Cosmetics & Toiletries, 95, 59 (1980), states that the factors affecting drug penetration and, consequently, in most cases, effectiveness, are complex. He observes that the vehicle that provides ideal conditions for one drug may prove unsatisfactory for another. The author concludes that prediction is not simple and product suitability must be assessed by human trials. The same article indicates that Synalar Cream, a topical corticosteroid preparation, contains sorbitan monooleate and propylene glycol.
M. M. Rieger, Cosmetics & Toiletries, 94, 32-37 (1979) and 95, 26-38 (1980), provides a review of current literature in the area of skin penetration.
U.S. Pat. No. 4,299,826, Luedders, issued Nov. 10, 1981, describes a composition for the treatment of acne by using diisopropyl sebacate as a penetration enhancer for an erythromycin derivative in combination with an alcohol.
U.S. Pat. No. 2,990,331, Neumann, et al., issued June 27, 1961, describes the parenteral administration of tetracycline salts from a stable aqueous solution.
CA 79: 122,308, describes an electromagnetic study of n-alkyl ionic surfactants as aiding in human epidermis penetration.